The present invention relates to the field of optical testing of laser beams. More specifically, it concerns testing of laser beam profilers and analyzing power distribution in a perpendicular direction to the laser propagation axis.
Designing, building, and/or using laser systems requires instrumentation for measuring the laser beam characteristics.
It is particularly useful to measure the beam intensity profile across the transverse area of the beam at any selected position. The beam intensity distribution across the transverse plane is a two-dimensional mapping of the beam intensity across and perpendicular to the beam length.
Much effort has been dedicated towards the measuring and standardization of beam profilers and their distribution. Two main technologies are available: those which use spatial cameras as the beam characterization system, and systems using moving mechanical slits or knife edges to scan across the incoming beam.
Both technologies are well described at the 1998/1999 Coherent Catalog for Laser and Photonic Applications (Coherent Auburn Group, USA).
The main advantages of mechanical scanning devices over a camera type system is their large dynamic range, enabling accurate measurements of beams with both high and low intensities.
On the other hand, camera type systems are excellent for fast and detailed analyses of laser beam intensity profiles, but are limited in their accuracy due to a relatively low dynamic range.
It is an object of the present invention to overcome the limited dynamic range of a camera type beam profiler and accurately measure faint structures of light beams including laser beams and coherent beams, by sampling the beam plural times (at least twice), each sampling being performed at a different attenuation or electronic shutter.
It is another object of the present invention to overcome difficulties of the prior art, such as indicated above, and more especially the lack of dynamic range in a camera based system to allow examination of faint features at the base of the laser beam profile.
It is a further object of the present invention to provide improvements in the testing of laser systems as well as in testing other light sources.
In accordance with the present invention, a video camera apparatus is provided, which is suitable for measuring beam power spatial distribution at an increased dynamic range revealing and measuring faint spatial power features. The laser, or the light beam to be analyzed, is imaged through a filter or an electronic shutter by a Charged Coupled Device (CCD) or other video camera and the amount of energy on each of the video camera pixels is recorded to obtain an original or reference image, and then digitized and transferred to a host computer for further processing.
The electronic shutter or optical filter, is tuned in such a way that none of the imaging pixels is saturated (i.e. saturation is defined as the stage where additional laser power on the same pixel will not generate additional proportional electronic signal).
The electronic shutter or optical filter is then removed, or the attenuation is significantly reduced, and the laser or the light beam is examined a second time by referably the same video camera to obtain a second image.
Due to the fact that the impinging power on the detection surface during the second examination is significantly higher, some of the image pixels will then be saturated. Some other pixels which at the original filter setting were below the digitization level will then be clearly displayed and analyzed.
The beam profiles are analyzed by using multiple images (a minimum of two), each one being attenuated by a different known factor which will be a part of the calculation to measure the beam intensity profile. The calculation, in percentages, will be generated with regards to the original non-saturated picture. Each faint pixel which originally was undetectable will be calculated by its energy value divided by the attenuation factor of the filter or electronic shutter.